Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Thu, 13 Jul 2017 15:34:16 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" |
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On Thu, Jul 13, 2017 at 11:20:04PM +0300, Andrey Rybainin wrote: > On 07/13/2017 09:47 PM, Matthias Kaehlcke wrote: > > > Thanks for your analysis! > > > >> What happens if you try the below patch instead of the revert? Any > >> chance the offending instruction goes away? > >> > >> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h > >> index 11433f9..beac907 100644 > >> --- a/arch/x86/include/asm/uaccess.h > >> +++ b/arch/x86/include/asm/uaccess.h > >> @@ -171,7 +171,7 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) > >> might_fault(); \ > >> asm volatile("call __get_user_%P4" \ > >> : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ > >> - : "0" (ptr), "i" (sizeof(*(ptr)))); \ > >> + : "0" (ptr), "i" (sizeof(*(ptr))), "r" (__sp)); \ > >> (x) = (__force __typeof__(*(ptr))) __val_gu; \ > >> __builtin_expect(__ret_gu, 0); \ > >> }) > > > > The generated code is basically the same, only that now the value from > > the stack is stored in a register and written twice to RSP: > > > > AFAIR clang works much better with global named registers. > Could you check if the patch bellow helps?
And yet another one to try (clobbering sp) :-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 11433f9..21f0c39 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -166,12 +166,12 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) ({ \ int __ret_gu; \ register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \ - register void *__sp asm(_ASM_SP); \ __chk_user_ptr(ptr); \ might_fault(); \ - asm volatile("call __get_user_%P4" \ - : "=a" (__ret_gu), "=r" (__val_gu), "+r" (__sp) \ - : "0" (ptr), "i" (sizeof(*(ptr)))); \ + asm volatile("call __get_user_%P3" \ + : "=a" (__ret_gu), "=r" (__val_gu) \ + : "0" (ptr), "i" (sizeof(*(ptr))) \ + : "sp"); \ (x) = (__force __typeof__(*(ptr))) __val_gu; \ __builtin_expect(__ret_gu, 0); \ })
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